The invention relates to a clamping device with a tensioning lever and a tensioning nut. The tensioning lever has a seat with a noncircular internal shape for receiving the tensioning nut, which is mounted axially displaceably in the seat and has a correspondingly shaped external contour.
Clamping devices of the type mentioned are used for the non-positive bracing of at least two parts, which can be moved relative to one another. By applying a torque to a tensioning nut by means of a tensioning lever, the clamping device exerts or releases a clamping effect, depending on the direction of action of the torque. For example, the tensioning nut may be screwed onto a bolt with an external thread. When a tensioning effect is exerted, the parts are pressed against one another and clamped by the thereby resulting frictional force. In the case of electric tools, especially in the case of manually guided circular saws, such clamping devices are used for fixing the angle of inclination between a stop plate and a working unit. In the absence of a clamping force, the angle of inclination can be adjusted and fixed in the desired position with the help of the clamping device. By these means, the user is enabled to carry out miter cuts or the like with the electric tool.
Such a clamping device is disclosed in the DE 197 36 933 A1. This known clamping device has a tensioning lever and a tensioning nut. The tensioning lever is provided with a seat with a noncircular internal shape for the tensioning nut, which is mounted axially displaceably therein. The external shape of the tensioning nut corresponds to the internal shape of the seat.
Through the use of a tensioning lever in the known clamping device, the user has at his disposal the lever action of the tensioning lever for exerting the clamping effect. With this, the user is enabled to act with a large torque on the screw connection, which is formed by the tensioning nut. It is a disadvantage of this known solution that the tensioning lever must always be taken along by the user.
Furthermore, in German patent 295/13/33 0, a clamping device with a tensioning lever and a screw connection is known. The screw connection has a screw, which is provided with a cross slot. Advantageously, the tensioning lever is fixed at the electric tool and therefore does not have to be carried along by the user. In addition, the clamping lever enables the clamping device to be operated without a tool.
It is a disadvantage of this known solution that the clamping device, mounted at poorly accessible places on the electric tool, makes complete bracing impossible. Furthermore, the tensioning lever may greatly impede the positioning of the electric tool in an exposed position.
It is an object of the present invention to create a clamping device for electric tools, which can be operated conveniently and safely by the user and, furthermore, can be manufactured economically.
Pursuant to the invention, this objective is accomplished owing to the fact that the tensioning lever has a tensioning cam, which can be disengaged against the force of a spring from the clear axial projection of the seat and, in the engaged state, is supported axially at the tensioning nut.
Due to the elastic tensioning cam, which can be disengaged, the tensioning lever can easily be removed from the tensioning nut. Furthermore, a user need not constantly carry along the tensioning lever and, instead, can leave it at the clamping device. If the tensioning lever is in an exposed position at the electric tool, the user can remove it and deposit it at the electric tool at a location intended for this purpose, loosen it and mount it once again at the position that is not exposed or take it along. Moreover, by repeatedly tightening and putting into place the removable tension lever, the user can brace the clamping device even in tight space conditions for the tensioning lever. The noncircular shape of the seat, together with the external shape of the tensioning nut, brings about a positive connection and thus enables the torque acting on the tensioning lever to be transferred. Instead of the tensioning nut, it is, of course also possible to use a different screw connection. For example, a screw with an external shape, constructed to correspond with the internal shape of the seat, can be used.
Advantageously, in the engaged state, the tensioning cam is supported in a recess of the tensioning nut, in order to prevent axial movement of the tensioning nut relative to the tensioning lever in the engaged state. In contrast to a frictional connection, this positive connection, ensures a reliable, removable connection between the tensioning nut and the tensioning lever. In addition such a solution enables the clamping device to be manufactured economically.
The recess is constructed preferably as an annular groove extending over the periphery of the tensioning nut. By these means, it can be ensured that, in the engaged state of the tensioning cam, the latter engages the recess, especially the groove, independently of the torsional angle between the tensioning nut and the tensioning lever.
In a preferred embodiment, the end region of the tensioning cam, spaced from the seat, is hinged to the tensioning lever. For example, the connection in the end region may be brought about by an elastic material such as rubber or the like. A different possibility consists of connecting the end region of hinging to the tensioning cam by means of a bolt with the tensioning lever. In the case of such an arrangement, the spring force can be applied by a spring or a flexible tongue. In particular applications, the tensioning cam may, of course, also be hinged in a different region to the tensioning lever.
Advantageously, an end region of the tensioning cam is connected by material retention with the tensioning lever, in order to achieve the elastic property of the tensioning cam relative to the tensioning lever. However, in order to be able to use a solid material for the tensioning cam, this connection must be as far away as possible from the seat for the tensioning nut. If such a high stability is not absolutely essential in certain applications, the material retention connection between the tensioning cam and the tensioning lever may also be disposed closer to the seat.
The tensioning cam may also be separated partially from the tensioning lever by an air gap, in order to develop the least friction during a movement of the tensioning cam relative to the tensioning lever. However, when soft materials are used for the tensioning cam, friction may be undesirable or even obligatory for the functioning. In such arrangements, other materials may, of course, also be disposed between the tensioning lever and the tensioning cam.
Preferably, the tensioning lever and the tensioning cam are formed from a plastics material. An economic manufacture of the tensioning device is assured with this distinguishing feature.